1. Field of the Invention
The present invention relates to a flexible, fast processing, photopolymerizable composition and to a sheet or roll prepared from the composition. The present invention also relates to a coated composition comprised of the flexible, fast processing, photopolymerizable composition on a substrate and to a process for making a printed circuit board using the flexible, fast processing, photopolymerizable composition.
2. Description of the Prior Art
Photopolymerizable compositions have long been known in the art. During their evolution, various chemical compounds have been used as a photopolymerizable component of the composition. One development in the art is disclosed in U.S. Pat. No. 2,760,863. This patent relates to a photopolymerizable composition useful in the preparation of printing plates which is comprised of an ethylenically unsaturated, photopolymerizable monomer, a photoinitiator, a polymerization inhibitor and a polymeric binding agent. The composition is coated onto a substrate, dried, exposed to actinic radiation through a stencil or negative and developed to remove the unexposed portions of the composition thereby forming the printing plate.
U.S. Pat. No. 3,469,982 marks an advance over the photopolymerizable composition described in U.S. Pat. No. 2,760,863. Rather than being applied as a liquid, this later patent discloses a photopolymerizable composition which is coated onto a flexible film base or support and then covered with a removable cover film. In use, the cover film is peeled off, the photopolymerizable composition is laminated to a substrate, exposed to actinic radiation through a negative, the film support is peeled off and the composition is developed in an organic solvent. To form a printed circuit board, the developed composition on the substrate is then subjected to etching and finally stripped in another organic solvent.
In U.S. Pat. No. 3,036,914, a photopolymerizable composition having improved flexibility which is useful for preparing printing plates is disclosed. The composition is comprised of: (1) an addition polymerizable, ethylenically unsaturated compound, such as diacrylates and acrylic or methacrylic acid esters of polyalkylene glycols; (2) a photoinitiator; (3) a high molecular weight polyethylene oxide; and (4) at least one essentially linear cellulose ester.
Improved flexibility is also the goal of U.S.S.R. Pat. No. 190,211. This goal is allegedly achieved by a photopolymerizable composition comprised of a photopolymerizable oligomer, a photoinitiator and a mixture of copolymers; the first being a copolymer of methacrylic acid and methyl methacrylate and the second being a copolymer of methacrylic acid or acrylic acid with butyl acrylate, alkyl methacrylate or alkyl acrylates containing 5 to 8 carbon atoms in the alkyl group.
In U.S. Pat. No. 3,887,450, and divisional U.S. Pat. No. 3,953,309, a significant advance in the art is set forth. These patents disclose a photopolymerizable composition which can be made into a storable sheet or roll on a film support. The composition may be used to prepare a printed circuit board and yet can be developed and stripped using aqueous solutions containing an alkaline agent. The photopolymerizable composition is comprised of a photopolymerizable ethylenically unsaturated monomer, a photoinitiator, a polymerization inhibitor and a binding agent which is a polymer of one or more of a defined styrene or vinyl monomer with one or more of a defined alpha, beta-ethylenically unsaturated carboxylic acid- or anhydride-containing monomer. The ratio of the monomers is selected to yield the required performance characteristics.
A further advance in the art is disclosed in U.S. Pat. No. 4,239,849. This patent describes a flexible photopolymerizable composition that is resistant to cold flow which may be formed into a dry film on a film support and, after exposure to actinic radiation, which may be developed in dilute aqueous alkaline solutions. The composition is comprised of one or more additional polymerizable, ethylenically unsaturated compounds, a photoinitiator and a preformed macromolecular polymeric binding agent. The binding agent is a copolymer of a styrene-type monomer, an acrylate-type monomer and an unsaturated carboxyl-containing monomer.